The present invention relates to a package for carrying a semiconductor chip for high-power and high-frequency applications and to a semiconductor device composed of the semiconductor chip for high-power and high-frequency applications mounted on the package.
In recent years, there has been increasing demand for high-frequency semiconductor devices such as a MESFET composed of gallium arsenide (GaAs) that has been used more prevalently in consumer products with the development of mobile communication. In the field of the high-frequency semiconductor devices, the use of the microwave or milliwave band as a replacement for the VHF or UHF band has been desired for the achievement of higher-quality communication and effective use of frequencies. To implement a communication system using such a high-frequency band, it is important to develop, as an RF amplifier, a semiconductor device for high-power and high-frequency applications which is easy to mass produce.
However, the conventional high-frequency semiconductor devices using the high-frequency band, such as the GaAs transistor, have been developed exclusively for use in defense industry and other special-purpose application areas. Since mobile communication requires particularly high power, considerably advanced and complicated mounting technology is necessary to apply the high-frequency semiconductor devices to the field of mobile communication, which presents a serious problem associated with the mass-producibility of the semiconductor devices.
Referring to the drawings, a conventional semiconductor device composed of a semiconductor chip for high-power and high-frequency applications mounted on a package will be described.
FIGS. 4 illustrate the structure of the conventional semiconductor device composed of the semiconductor chip for high-power and high-frequency applications mounted on the package, of which FIG. 4(a) shows a plan structure and FIG. 4(b) shows a cross-sectional structure.
As shown in FIGS. 4(a) and 4(b), two semiconductor chips 11 including transistors for high-power and high-output applications, such as MESFETs formed on a GaAs substrate, are mounted on the central portion of a heat radiator 10 made of metal such as copper, which is to serve as a heat sink. On both sides of each of the semiconductor chips 11, two circuit boards 12 made of ceramic or the like are mounted on the heat radiator 10. On each of the circuit boards 12, there are formed a power distributing/synthesizing circuit, an I/O impedance matching circuit for the transistor, and surface wiring for providing connection between the power distributing/synthesizing circuit and the I/O impedance matching circuit.
On the left edge portion of the heat radiator 10, an input lead 13 and an input wiring pad 14 integrally formed with the input lead 13 are disposed via an insulator 15. On the right edge portion of the heat radiator 10, an output lead 16 and an output wiring pad 17 integrally formed with the output lead 16 are disposed via the insulator 15.
The semiconductor chips 11 and the circuit boards 12 are connected to each other by first bonding wires 18 for signal transmission. The circuit boards 12 and the input wiring pad 14 are connected to each other by second bonding wires 19 for signal transmission, while the circuit boards 12 and the output wiring pad 17 are also connected to each other by the second bonding wires 19 for signal transmission. A surrounding wall member 20 made of ceramic or the like and shaped like a square frame is formed on the input and output leads 13 and 16 overlying the insulators 15. It is to be noted that the input and output leads 13 and 16 extend through respective cut-away portions formed in the surrounding wall member 20.
FIG. 4(c) shows a cross-sectional structure of a portion different from the one shown in FIG. 4(b) of the semiconductor chip 11. A MESFET 23 made of GaAs is formed in the surface region of the semiconductor chip 11. The MESFET 23 has a drain connected to the first bonding wire 18 and a source connected to a gold plating layer 22 formed on the back face of the semiconductor chip 11 via a conductive material filled in a via hole 21 extending through the semiconductor chip 11. The purpose of connecting the source of the MESFET 23 to the gold plating layer 22 via the conductive material filled in the via hole 21 is to reduce a grounding line and thereby prevent the deterioration of the high-frequency gain of the MESFET 23.
In the case of forming a high-power transistor on the semiconductor chip 11, the thickness of the semiconductor chip 11 should be reduced to the order of several tens of micrometers so as to reduce thermal resistance in the semiconductor chip 11 in transmitting heat generated from the high-power transistor to the heat radiator 10. In short, the thickness of the semiconductor chip 11 formed with the high-power transistor should be reduced significantly.
This leads to the problems that an advanced manufacturing technique is required to form the via hole 21 in the semiconductor chip 11 and that the production yield lowers during the processing of the semiconductor chip 11.
In the case where numerous via holes 21 are formed in the semiconductor chip 11 with an extremely reduced thickness, the semiconductor chip 11 to be mounted on the heat radiator 10 should be handled with extreme caution and attentiveness because of its reduced mechanical strength, while the cracking of the semiconductor chip 11 lowers the production yield during the mounting of the semiconductor chip 11.
In the case where the semiconductor chip 11 is made of a fragile material such as GaAs, in particular, the lowering of the production yield during the processing and mounting of the semiconductor chip 11, as described above, presents an extremely serious problem.